A 74-year-old woman presented with a 6-week history of progressive dyspnea on exertion. Eight weeks before this presentation, she had been traveling in Italy and had been walking up to 4 miles per day. Progressive dyspnea on exertion had developed after she returned to the United States. She also noted a nonproductive cough, fatigue, loss of appetite, and an unintentional weight loss of 9 kg over the previous 6 months. She had no fevers, chills, night sweats, hemoptysis, wheezing, chest pain, palpitations, orthopnea, paroxysmal nocturnal dyspnea, swelling of the legs or feet, abdominal pain, nausea, vomiting, melena, or hematochezia. Four weeks before this presentation, she had presented to an emergency department at another institution, where imaging was performed. Chest radiography showed no pneumonia, and venous ultrasonography of both legs showed no deep venous thrombosis. A 5-day course of prednisone and azithromycin was prescribed; however, her symptoms continued to worsen, and she began to have dyspnea when she was at rest.